Evidence from animal models of arterial hypertension suggests a hypotensive effect of dietary calcium on blood pressure (BP). However, epidemiologic and clinical studies in humans have yielded mixed results. A review of this literature indicates that an inverse relation between dietary calcium and BP is most evident among US blacks and youth, while it is small or absent among adult whites. A plausible explanation of this pattern of findings is that the effect of dietary calcium on BP occurs early in the life cycle. Thus, it is hypothesized that dietary calcium supplementation among black youth will blunt the rise in BP that occurs after puberty in US blacks (which is coincident with he decline in consumption of dairy products in this population). In order to set this hypothesis a double blind, cross over, placebo controlled trial among black adolescents is proposed. High school students screened for elevated BP (N=100) in an ongoing BP monitoring program will be randomized to 8 week calcium supplementation (1500 mg/d) and placebo conditions during the Fall school semester. Cross-over will occur during the Spring semester. Supplements will be administered by school nurses to allow precise dosage measurement. Effects of the calcium supplementation will be assessed by change in SBP and DBP measured by standard and ambulatory methods. In Years 2 and 3 of the study, those students remaining in the school will be assessed for the reproducibility of apparent calcium sensitivity observed in Years 1 and 2. Concurrent changes in plasma concentrations of parathyroid hormone, total and ionized calcium, and other correlates of BP will be measured. If calcium supplementation is successful in blunting the age related BP rise in this population, then health protective policies aimed at calcium supplementation of commonly ingested foods could ameliorate some of the excess risk of hypertension among US blacks.